FULL TA GAME WALKTHROUGH F/ 1000G NOW LIVE. Thanks For this achievement, you must watch the credits after a full play through.
Since for the full 1000G you will be playing the game from the start to the end credits twice, this should come naturally at the end of your first play through.
Simple achievement, but due to the cryptic nature of this game (achievements and, well, everything else) no achievement is "self explanatory" as such.
EDIT: SanJol in the comments has also kindly pointed out that any use of chapter select will void the achievement. Best to just stick to doing it all in one playthrough, guys.